EP2815207B1 - Method for measuring the distance between two objects - Google Patents

Description

The invention relates to a method for optically measuring the distance between an object which differs optically substantially and an object which is optically substantially reflective by means of a light line using at least one light source and at least one light receiver.

Optical distance measuring methods, such as laser distance measurements by means of interference or transit time measurement, light-section method or other triangulation methods are known. In order to obtain evaluable light signals in this case, the light source and in relation to the light receiver must be positioned in a certain way to obtain sufficiently strong, evaluable light signals that allow a distance measurement.

Light-section methods are known as metrological methods for measuring the height profile of surfaces along a projected light line and are used industrially for many applications. They are based on the principle of triangulation. For this it is necessary that the light source, light receiver and test sample form a triangle. The greater the angle between the optical axes of the transmitting. and receiving optics, the greater the height resolution of the measuring arrangement. The projected onto an object line of light undergoes a deformation by the surface contour of the object, which is recorded and evaluated with a camera as a light receiver. The greater the angle between the light source and the light receiver, the stronger the deformation of the light line in the light receiver is visible. The known light-section method is also dependent on that the surface of the object to be measured has sufficiently light-scattering properties, so that a part of the incident light on the surface of the object is diffused to the receiving camera. However, if the surface is specular or specular in some areas, the specular reflection on the surface dominates there. This mirror reflex is in space do not meet the receiver optics, so that no usable signal hits the receiver.

In some applications, the application of these conventional methods for determining the distance between two objects is not possible if due to specific geometrical conditions no evaluable signals or only non-specific signals for determining the distance between a substantially scattering object and a substantially specular object are.

For example, the conventional optical distance measuring methods are not usable when one of the objects has a reflective surface, while the other object scatters the light, as is the case, for example, in crystal pulling systems for producing monocrystalline silicon crystals, so-called ingots, where the distance between an im Essentially scattering object, a funnel surrounding the ingot, and a substantially specular object, a hot silicon melt to be measured.

From the pamphlets US 2010/0165321 and US 6 572699 B1 are measuring devices and measuring methods are known in which a distance measurement in connection with crystal pulling method by measuring pointwise distances is made by triangulation. The overall result is composed of results of several temporally successive individual measurements at various defined points.

The publication US 2004/0095584 A1 describes a method and apparatus for measuring the distance of a nozzle from a specular sheet metal part. Here, a laser light line is projected parallel to the sheet metal part and parallel to the nozzle edge on the nozzle. The laser light line lies exclusively on the scattering object of the nozzle. By recording two parallel Light lines, the distance between these two lines of light in the camera image is evaluated to determine in this way indirectly the distance of the nozzle exit from the sheet metal part.

The invention has for its object to provide a measuring method, with which it is possible to measure the distance between a substantially scattering and a substantially specular object even under difficult geometrical and lighting conditions, such as crystal pulling process, the distance between a substantially.

This object is achieved by a method according to claim 1. Advantageous developments of the invention are the subject of the dependent claims. The line of light includes both at least a portion of the diffusing and at least a portion of the specular article, and both the light scattered at the diffusing object and the specular reflected light of the light line is evaluated and evaluated to determine the distance, the scattering at the diffusing object After reflection, the light reflected on the object to be mirrored and the light reflected at the specular object are picked up and evaluated after scattering on the scattering object.

In contrast to known light-slit methods, which are based on the principle of triangulation, in the present inventive method it is not necessary for the light source, the light receiver and the test sample to form a triangle. In the method according to the invention, the deformation of the light line, ie the light section, is not measured through the surface contour of the test sample. On the contrary, it is even advantageous if the distance between the light source and the light receiver is very small, or even paraxial, which can be achieved, for example, by a beam splitter which superimposes the optical axes of the light source and the light receiver. In the paraxial case, the optical axes of light source and light receiver coincide. The light line appears in this case from the perspective of Light receiver always as a straight line, no matter how pronounced the height profile of the object is, on which the light line hits. The inventive method is based on the fact that additional reflections occur by reflection on the specular object, which can then be evaluated in the image recorded by the light receiver. These additional reflections continue to geometrically separate as the distance between the scattering object and the specular object increases.

A particularly advantageous embodiment of the method according to the invention consists in that the scattering object has a chamfer on the edge of the end facing the specular article and that the light scattered thereon is recorded and evaluated. This results in geometrically defined reflections and specular reflections of the guideline at the chamfer, which then allow a precise evaluation of the light receiver detected image, such as a camera image.

It is also advantageous to rotate the light line obliquely to the vertical. As a result, the occurring reflections and mirror reflections are offset from one another horizontally and facilitate the evaluation of the image determined by the light receiver through this geometric separation.

It is very advantageous according to a further embodiment of the invention, when the light source emits light in a predetermined wavelength range, preferably in a violet, blue and / or green wavelength range. Advantageously, the wavelength recording range of the light receiver is limited depending on the wavelength range of the light source, preferably by means of a bandpass filter. A preferably narrow-band wavelength range of the light receiver in the short-wave spectral range below 550 nm with preferably high intensity of the light source in this wavelength range has particular advantages. It has been found in connection with these measures that a black body radiation of the specular object, such as in a hot silicon source, can be damped very effectively, thereby dominating the light evaluated for the measurement in comparison to the filtered out black body radiation, resulting in simpler and more accurate spacing. Results in measurements.

Preferably, the light receiver is a digital or matrix or line scan camera.

In order to determine not only the distance but also the skew between the scattering and reflecting objects, it is advantageous to determine the distance to at least two locations selected between the objects.

The method according to the invention can be used particularly advantageously in connection with crystal pulling systems in which the essentially scattering object is a funnel surrounding an ingot and the object which essentially reflects is a hot silicon melt.

Monocrystalline silicon wafers are required for the production of monocrystalline silicon solar cells. The most important method for producing these wafers is that a monocrystalline ingot is slowly drawn from a hot silicon melt, for example by means of the so-called Czochralsky crystal pulling method. Due to the slow crystal growth, this process usually takes several days. The crystal is then cut to size and then sawn into wafers with sawing machines, which are then further processed to produce the solar cells.

The Czochralsky crystal pulling process is a sensitive process that often leads to structural breakage of the crystal. Then the drawing process has to be aborted and started again. Process instabilities can also lead to crystal diameter fluctuations or to a quality-reducing increased number of defects in the crystal. Or the crystal has to be pulled at a slow pull rate due to process instabilities.

For the crystal pulling process, it is particularly important to ensure thermally stable conditions of the hot silicon melt and the air space above the melt during the drawing process in the Czochralsky plant. This is important in order to prevent a break in the structure of the monocrystal, in order to be able to maximize the pulling speed of the crystal and to obtain as constant a diameter of the ingot as possible over the height. In order to achieve an improved stability of the temperature distribution in the Czochralsky plant mostly funnel-shaped inserts are used, which surround the ingot cylindrically symmetric and which reach with the lower edge of the funnel as close as possible to the melt. The control of the distance of the lower edge of the funnel from the melt is an important Process parameters. However, it is difficult to precisely control and regulate this distance. This distance should be very small without touching the melt and should be kept constant during the drawing process, or possibly even changed in a predefined manner during the drawing process. For the maintenance of the desired distances between funnel and melt or the distance control method of the invention is particularly well suited.

With the conventional optical measuring methods, the distance measurement is difficult, because only an insight on sight glasses from an unfavorable perspective from obliquely above, even at a very steep angle, in the chamber with the melt is possible, and because the high temperatures and the self-luminous Melting at about 1500 ° C make an optical measurement enormously difficult. With the method according to the invention, this difficulty and limitations are overcome.

Fig. 1

eine schematische Querschnittsdarstellung einer Czochralsky-Kristallziehanlage;

Fig. 2

die in Fig. 1 dargestellte Anlage in perspektivischer Darstellung;

Fig. 3 bis 5

schematische Lichtstrahlverläufe zur Erläuterung des erfindungsgemäßen Verfahrens;

Fig. 6

Strahlenverläufe im Falle einer besonderen Ausführungsform, bei der der Rand des streuenden Gegenstands, im vorliegenden Fall des Trichters, eine Fase aufweist;

Fig. 7

eine vergrößerte Darstellung der in Fig. 6 gezeigten Ausführungsform mit schematischen Strahlverläufen; und

Fig. 8

einen vergrößerten Ausschnitt aus Fig. 2 in Blickrichtung des Lichtempfängers.

The method according to the invention and its advantages are or will be explained in detail below with reference to a crystal pulling apparatus as an exemplary embodiment. Show it:

Fig. 1

a schematic cross-sectional view of a Czochralsky crystal pulling system;

Fig. 2

in the Fig. 1 illustrated plant in perspective view;

Fig. 3 to 5

schematic light beam courses for explaining the method according to the invention;

Fig. 6

Beam paths in the case of a particular embodiment in which the edge of the scattering article, in the present case of the funnel, has a chamfer;

Fig. 7

an enlarged view of in Fig. 6 shown embodiment with schematic beam paths; and

Fig. 8

an enlarged section Fig. 2 in the direction of the light receiver.

Fig. 1 shows a section of a Czochralsky crystal pulling system with safety container 8, hot silicon melt 3 in a crucible 7, which can be moved vertically by a lifting device 6, a monocrystal (ingot) 2 during the drawing process, a funnel 1, which surrounds the crystal 2 cylindrically symmetric and with its lower edge up to a free distance d of a few millimeters reaches the melt 3. In an advantageous arrangement, a light source 4 and a receiving camera 5 are arranged as close as possible next to each other and look through the same sight glass 9. However, it is also possible to further space light source 4 and receiver 5 and to be attached to two separate sight glasses.

Fig. 2 shows the same arrangement in the direction obliquely from above. Shown here is a light line 10 projected by the light source 4 and received by the camera 5, which includes both the lower edge of the funnel 1 and the part of the silicon melt 2 adjoining the funnel edge. The light cones from the light source 4 and to the camera 5 are also shown.

The light reflections occurring in this arrangement, which are received and evaluated by the camera are in the FIGS. 3 to 7 shown schematically. In the Fig. 3 to 7 For the sake of greater clarity, it is assumed that the optical axes of light source 4 and receiver 5 are paraxial with parallel opposite direction vectors L and K of transmitted (illuminating) and received (reflected) light beams, the transmitted light beams being parallel, narrow Light beam (light line) and only parallel light, which is backscattered or reflected back in the same direction as the transmission beam, is received by the receiving camera 5.

In addition, it is assumed for simplicity that the light line 10, the irradiation direction L and the direction of arrival K of the light, and the normal vector of the funnel 1 along the line of incidence of the light line 10, all in the Lying on the drawing plane. This is in Fig. 3 shown. Here, the funnel 1, the silicon melt 3 with a reflective surface 11 can be seen. The funnel 1 encloses an angle α with the normal vector on the silicon melt 3 and has a free distance d from the surface 11 of the silicon melt 3. The parallel light beam irradiated from the direction L forms a line in the plane of the drawing. This continuous light line 10 is here represented by seven light beams 13, 14, 15, 16, 17, 18, 19 (from left to right), the distance from beam 13 to beam 19 indicating the length of the light line.

Perpendicular to the plane of the drawing, the extension of the light line 10 is assumed to be negligibly small. The irradiation direction L encloses an angle β with the normal vector on the surface 11 of the silicon melt 3.

In the FIGS. 3 and 4 applies to the angles α and β: α <β. The beams 13, 14, 15 impinge directly on the funnel 1 and are scattered there on the rough surface of the funnel 1. The proportions of scattered light scattered in direction K, as in Fig. 4 can be seen are received by the camera 5 and are therefore visible in the camera image. This beam path is referred to below as LTK (light source funnel camera).

In Fig. 4 For example, the point of impact of beam 13 on the hopper 1 is shown at which the light is scattered in all directions. Therefore, a part of the light of the beams 13, 14, 15 is scattered in the direction of silicon melt 3 and reflected there mirroring. The components of the light reflected there, which is reflected in direction K, are the beams 20, 21, 22 in FIG Fig. 4 , They are received by the camera 5 and are therefore visible in the camera image. This beam path is referred to below as L-TS-K (light source funnel-melt camera).

• L-T-K (Lichtquelle-Trichter-Kamera)
• L-ST-K (Lichtquelle-Schmelze-Trichter-Kamera)
• L-TS-K (Lichtquelle-Trichter-Schmelze-Kamera)
• L-STS-K (Lichtquelle-Schmelze-Trichter-Schmelze-Kamera)

How out Fig. 5 or 6 can be seen, the beam 16 hits the surface 11 of the silicon melt 3 and is reflected from there behind the hopper 1 specular. This reflex is not visible from the camera 5. The beam 17 strikes the surface 11 of the silicon melt 3, is reflected there mirror-like and then strikes the edge of the funnel 1 from below and is scattered there. The scattered light then hits again on the silicon melt 3, is partially reflected in the direction K to the camera 5 and is then also visible in the camera image. Although this reflex is basically usable for the evaluation, but due to the two-time reflection on the surface 11 of the melt 3 and less suitable for geometric reasons. This beam path is referred to below as L-STS-K. The rays 18 and 19 strike the surface 11 of the silicon melt 3, where they are reflected by reflection, and then hit the funnel 1. The portions of the light then scattered at the funnel 1, which are scattered in the direction K, are received by the camera 5 and can be seen in the camera image. This beam path is referred to below as L-ST-K (light source-melt funnel camera). The occurring beam paths, which deliver evaluable images of parts of the light line in the camera, are thus:

• LTK (light source funnel camera)
• L-ST-K (Light Source Melt Funnel Camera)
• L-TS-K (Light Source Funnel Melting Camera)
• L-STS-K (Light Source Melt Funnel Melting Camera)

Although the Reflex L-STS-K can be used for the evaluation, it is less suitable than the three other reflections because it is attenuated in intensity by the two-fold specular reflection on the melt 3 and has more interference due to the double reflection , In addition, the funnel 1 itself leads to a partial shading of this beam path when the distance d is small. Therefore, this beam path will be disregarded below.

• L-T-K: Die Intensität des in die Kamera 5 zurückgestreuten Signals wird durch die Streueigenschaften der Trichteroberfläche bestimmt. Wie in Fig. 4 zu sehen ist, sind die Abstände der einlaufenden Strahlen 13, 14, 15 identisch mit den Abständen der in die Kamera 5 zurückgestreuten Strahlen. Die Strahlenbündel liegen aufeinander. Daher gibt es keine perspektivische Kompression oder Expansion des empfangenen Strahlenbündels gegenüber dem beleuchtenden Strahlenbündel. Sowohl das beleuchtende, als auch das empfangene Strahlenbündel schließen einen Winkel β + α mit dem Trichter 1 ein.
• L-TS-K: Der Winkel des gestreuten Lichts mit dem Trichter 1 ist β - α, also sehr flach. Daher ist das zur Kamera reflektierte Lichtbündel perspektivisch um den Faktor sin(β-α)/sin(β+α) komprimiert, es erscheint im Kamerabild also verkürzt. Dies ist in Fig. 4 daran zu sehen, dass die Strahlen 20, 21, 22 deutlich dichter beieinander liegen, als die Strahlen 13, 14, 15.
• L-ST-K: Das Licht trifft nach Reflexion an der Oberfläche 11 der Schmelze 3 auf den Trichter 1 und schließt ebenfalls einen Winkel β - α mit dem Trichter 1 ein. Das unter dem Winkel β + α in die Kamera 5 gestreute Licht ist daher um den Faktor sin(β+α)/sin(β-α) perspektivisch verlängert. Dies ist in Fig. 3 an den weit auseinander liegenden Auftreffpunkten der an der Oberfläche 11 der Schmelze 3 reflektierten Strahlen 18 und 19 auf dem Trichter 1 zu sehen. Dadurch erscheint dieses Linienstück im Kamerabild perspektivisch verlängert und dadurch seine Strahldichte bzw. Helligkeit im Kamerabild erheblich abgeschwächt.

In the following, the geometric properties and the intensity properties of the three optical paths LTK, L-ST-K, L-TS-K are considered.

• LTK: The intensity of the signal backscattered in the camera 5 is determined by the scattering properties of the funnel surface. As in Fig. 4 can be seen, the distances of the incoming rays 13, 14, 15 are identical to the distances of the backscattered into the camera 5 rays. The bundles of rays lie on each other. Therefore, there is no perspective compression or expansion of the received beam with respect to the illuminating beam. Both the illuminating and the received beams include an angle β + α with the hopper 1.
• L-TS-K: The angle of the scattered light with the funnel 1 is β - α, thus very flat. Therefore, the light beam reflected to the camera is perspectively compressed by the factor sin (β-α) / sin (β + α), so it appears shortened in the camera image. This is in Fig. 4 to see that the beams 20, 21, 22 are significantly closer together than the beams 13, 14, 15.
• L-ST-K: The light strikes the funnel 1 after reflection on the surface 11 of the melt 3 and likewise encloses an angle β-α with the funnel 1. The light scattered into the camera 5 at the angle β + α is therefore extended in perspective by the factor sin (β + α) / sin (β-α). This is in Fig. 3 to see at the widely spaced impact points of reflected at the surface 11 of the melt 3 rays 18 and 19 on the hopper 1. As a result, this line piece in the camera image appears to be extended in perspective and thus considerably attenuates its radiance or brightness in the camera image.

The smaller the angular difference β - α, the less favorable are the geometric conditions and the intensity ratios for the measurement. The perspective compression and expansion of L-TS-K and L-ST-K increase for small values β-α, and their brightness differences in the camera image then also increase, which increases the demands on the dynamic range of the camera 5.

If the funnel angle α is greater than β, the reflexes L-TS-K and L-ST-K vanish completely. This is in Fig. 5 to see. In Fig. 5 is α> β. The rays 18 and 19 are no longer incident on the funnel 1. Also, the rays 20 and 21, as in Fig. 4 are shaded by the funnel 1. A measurement is not possible in this case.

In practice, the position of the sight glasses 9 and the funnel angles are predetermined by the plant constructor or by the operator of the drawing plants. As a rule, this limits the possible angle ranges for α and β very strongly and makes a measurement possibly even impossible. Then the arrangement according to the invention can not be used. However, this problem can be solved according to the invention in a particularly advantageous embodiment in that a vertical chamfer 12 is ground to the funnel 1 at the lower edge. This is in Fig. 6 and enlarged in Fig. 7 shown. In Fig. 7 only the beam paths over this chamfer 12 are shown. It can be seen here at the bidirectional beams 20, 21, 22 and 23, 24, 25 that the beam paths L-ST-K and L-TS-K are now completely symmetrical, and that the beams reflected at the melt always have an angle β with the normal vector and the rays scattered on the chamfer 12 always enclose an angle 90 ° -β with the normal vector on the chamfer 12. This applies in this very advantageous embodiment for all three beam paths LTK, L-ST-K and L-TS-K. As a result, the two reflections L-ST-K and L-TS-K in the camera image have the same brightness and the same length. The brightness of L-ST-K and L-TS-K is reduced only by a fixed factor compared to the brightness of LTK. This factor is the surface reflectance of the surface 11 of the melt 3, because in the beam paths L-ST-K and L-TS-K occurs an additional reflection on the surface 11 of the melt 3, which does not exist in the beam path LTK. Thus, the arrangement with bevel 13 on the hopper 1 is particularly advantageous because it creates stable and favorable geometric conditions and brightness conditions and makes the arrangement independent of the funnel angle of the hopper 1 and the position of the sight glasses. 9

For an evaluation of the beam paths LTK, L-ST-K and L-TS-K in the camera image, it is necessary that these beam paths are separated in the camera image. In the Figures 3 and 7 but it can be seen that LTK and L-ST-K are superimposed. This problem is solved according to a further embodiment of the invention in that the light line is rotated. In the FIGS. 3 to 7 the light line lies in the plane of the drawing, ie in the same plane, which is also spanned by the normal vector on the surface 11 of the melt 3 and the directional vector (optical axis) of the camera 5. If the line is rotated, however, the rays are 13 to 19 in Fig. 3 offset one behind the other perpendicular to the plane of the drawing and thereby also the beam paths LTK and L-ST-K are separated in this direction. This is true regardless of whether there is the normal vector on the hopper 1 in the drawing plane, or not. It is therefore also immaterial which area of the funnel 1 is illuminated with the light line. This is particularly important because the sight glass 9 opposite side of the funnel 1 is covered by the ingot 2 during the drawing process. Therefore, the measurement must be done on the left or right of the ingot 2 during the drawing process.

Fig. 8 shows enlarged the section with the light line 10 off Fig. 2 , but now exactly from the line of sight of the camera 5. Here is a section of the funnel 1 is shown. Additionally are in Fig. 8 the relevant mirror reflections on the surface 11 of the melt 3 drawn. In Fig. 8 the light line 10 is rotated in an advantageous manner and the lower edge of the hopper 1 has a chamfer of width F. The mirror image FR of the chamfer F on the surface 11 of the melt 3 is also shown. The distance between F and FR is proportional to 2d, where d is the distance between funnel 1 and melt 3, which is measured with the measuring arrangement. The section 30 of the light line illuminates the chamfer F and can be seen directly in the camera image. In addition, it is reflected as a mirror reflex 29 in the surface 11 of the melt 3, wherein the mirror plane 26 is spanned by the normal vector on the surface 11 of the melt 3 and the viewing direction of the camera 5. The portion 31 of the light line that on the area FR of the silicon melt 3 meets, is reflected in the melt and then meets as a reflex 28 on the chamfer F of the funnel 1. This reflection takes place along the mirror plane 27. The reflections 30, 29 and 28 are already based on the FIGS. 3 to 7 discussed beam paths LTK, L-ST-K and L-TS-K. As a result of the rotation of the light line, the beam paths L-ST-K, L-TS-K and LTK are offset laterally in the camera image, the offset being proportional to the distance d measured with the arrangement. In the special case that the light line 10 is not rotated, that is parallel to the mirror plane 26 (or 27), there is no lateral splitting. The irradiated light line and the beam paths 28, 29 and 30 are then unfavorably along a line and partially to each other for a measurement.

The measuring principles according to the invention described here remain valid even if the light source 4 and the camera 5 are not paraxial or even if they are clearly spaced from each other and thus enclose a large angle. This is e.g. then the case when light source 4 and camera 5 are attached to two separate sight glasses of the system. However, the geometric conditions and the evaluation of the beam paths in the camera image then become more complex.

The measuring principles according to the invention described here remain valid even if the camera 5 and the light source 4 do not work with parallel beams, but, for example, the illuminating light line 10 has a beam divergence in the plane of the line. This is the case, for example, when a laser with initially parallel beam is used as the light source 4 and this beam is then uniaxially widened to a diverging light line by means of a cylindrical lens.

In an advantageous embodiment of the invention, the measurement takes place in the short-wave spectral range, wherein the very intense and otherwise extremely disturbing thermal radiation of the silicon melt 3 is suppressed by a narrow-band bandpass filter in the camera 5. Advantageously, this is a laser in the short-wave spectral range, preferably in the blue or violet spectral range, and a narrowband bandpass filter matching the laser wavelength used in the camera optics.

According to the invention, instead of the light line, a point of light scanning along a line can also be used.

The process according to the invention has been described above using the example of a crystal pulling apparatus. However, the application of the method according to the invention is not limited to this application example, but can also be used advantageously in numerous other applications for determining the free distances of at least two objects under special and complicated geometrical and applicational conditions.

Claims (10)

1. Method for optically measuring the distance (d) between a substantially scattering object (1, T) and a substantially reflecting object (3, S) by means of a line of light (10) using at least one light source (4) and at least one light receiver (5), wherein the line of light (10) includes at least one region of the scattering object (1) and also at least one region of the reflecting object (3), characterized in that both a part-section of the line of light (10), which is firstly scattered at the scattering object (1) and thereafter is reflected at the reflecting object (3) (light path light source L - funnel T - melt S - camera K), is captured, then a part-section of the line of light (10), which is firstly reflected at the reflecting object (3) and thereafter scattered at the scattering object (1) (light path light source L - melt S - funnel T - camera K), is captured, and a part-section of the line of light (10), which is scattered at the scattering object (1) (light path light source L - funnel T - camera K) is captured, wherein the three part-sections are imaged displaced to each other in the light receiver (5), and this displacement which is proportional to the distance (d), is determined.
2. Method in accordance with claim 1, characterized in that the scattering object (1) has a chamfer (12) at the edge of the end thereof facing the reflecting object, and the light scattered thereat is captured.
3. Method in accordance with claim 1 or 2, characterized in that the line of light (10) is rotated horizontally to each other to the displacement of the occurring reflexes and mirror reflexes.
4. Method in accordance with any of the preceding claims, characterized in that the light source (4) emits light in a given wavelength range, preferably in a violet, blue and/or green wavelength range.
5. Method in accordance with claim 4, characterized in that the wavelength capture range of the light receiver (5) is limited in dependence on the wavelength range of the light delivered by the light source, preferably by means of a bandpass filter.
6. Method in accordance with claim 4 or 5, characterized in that the wavelength capture range of the light receiver (5) lies in a preferably narrow wavelength range smaller than 550 nm.
7. Method in accordance with any of the preceding claims, characterized in that a linear scanning light spot is used as the line of light (10).
8. Method in accordance with any of the preceding claims, characterized in that the light receiver (5) is a digital or matrix camera or a line camera.
9. Method in accordance with any of the preceding claims, characterized in that the distance between the scattering (1) and the reflecting object (3) is determined at at least two different positions for the purposes of determining an inclination.
10. Method in accordance with any of the preceding claims, characterized in that the scattering object (1) is a funnel surrounding an ingot and the reflecting object (3) is a hot silicon melt in a crystal pulling plant.

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